Well, I agree about the windows open, but I would never leave my kids in a running car!
Anyway, I think the county CPS guidelines for leaving kids alone applies to cars as well, so that mother was negligent if the oldest kid in the car was only 8.
http://www.fairfaxcounty.gov/dfs/childrenyouth/homealone.htm
Of course, with a car, you have the heat factor that you don't necessarily have in a home!! Yikes.